The Effect Of Water Stress On Fruit Quality And Citric Acid Metabolism Relative Gene Expression Of Citrus

Due to avoid the land utilization conflict with grain,oil and cotton crops,most of the citrus are cultivated in the hilly areas of south china,where the rainfall is uneven distributed, seasonal drought is serious,and soil preserving capacity of water and fertilizer is poor,citrus crops have to suffer from the shortage of water source,and also have strong impact on citrus production anf gruit quality.Citric acid is the main organic acids in citrus fruit, its synthetic pathway is mainly composed of the tricarboxylic acid cycle (TCA),while the degradation occurs primarily through the y-Aminobutyricacid (GABA) and Glutamine Synthase (GS) pathways.In this paper,Ponkan(C.reticulata) and Satsuma mandarin(C.unshiu Marc) were used as materials to study the effect of water stress on fruit quality and citric acid metabolism relative gene expression of citrus.The main results are as follows:1.Fruit quality was affected by plastic film mulching in field.Water control during the fruit cell division phase increased total sugar and reduced titratable acid content of fruit. Water control during the cell enlargement period can decrease total sugar and titratable acid content,and increase Vc content.Appropriate water control before harvest increased total sugar and Vc content,and decreased titratable acid content.2.Common Ponkan and Satsuma mandarin were used as materials to study the influence of the different stages of water stress on fruit exterior quality.The results showed that fruit size was influenced by water stress,and the impact of water strss on fruit size changed with water stress time and varieties.At harvest,Ponkan fruit weight,transverse diameter and longitudinal diameter indicated:CK>treatment â…¤>treatmentâ…¡>treatment â…£>treatment â…¢>treatment â… ,and Satsuma mandarin fruit weight,transverse diameter and longitudinal diameter indicated:CK and treatment â…¤> treatment â…£> treatment â…¡> treatment â…¢> treatment â… .Ponkan fruit size of the treatment II and Satsuma mandarin fruit size of treatment â…£ was the smallest in the all treatments.3.Water stress also influenced citrus interior quality,fructose,glucose and total sugar content of Ponkan fruit increased in all treatments,except the treatment â…¢,but sucrose concentration was reduced by all treatments.Major sugar content in the Satsuma mandarin fruits were increased significantly by all treatments.Only in treatment V,the total sugar content in each single fruit of both two cultivars was higher than that in control.The concentration of major organic acids in the Ponkan fruit was increased significantly by all treatmens,total organic acid content of each single fruit in treatment â…¡ and treatment â…¤ was significantly higher than that in CK.Organic acid concentration of Satsuma mandarin fruit was significantly increased under water stress,total organic acid content of each single fruit in treatment V was significantly higher than that in CK.4.Common Ponkan was used as materials to study the expression change of gene that related to citrate metabolism.The results showed that the relative expressions of CitCSl,CitCS2 was up-regulated,and they can portly recovered only under treatment â…¡ after watering again.Speculated that CS gene family was more sensitive to water stress in cell enlargement stage than cell division phase.The relative expression of CitAcol appeared up-regulation,expression of CitAco2 change with different treatments,the relative expression of CitAco3 was down-regulated under water stress.CitIDH3 was started at the earliest step, and expression was significantly up-regulated,expression of CitIDH3 change with different treatments,the relative expression of CitIDH2 was enhanced,and the expression of CitIDH3 was restrained.Expression of CitGAD (CitGAD4-5) genes were also restrained,but the impact to CitGAD5 was more significant.To sum up,water stress leaded to the accumulation of citric acid in different citrus varieties fruit,total organic acid was increased and total sugar was decreased,and the ratio of sugar and acid decreased.Organic acid content in the citrus fruits was limited by the metabolism rate of citric acid,and the metabolism rate of citric acid was regulated by the related genes.The reason of accumulation of citric acid under water stress is the expression of CitAco3,CitIDH3,CitGAD4 and CitGAD5 in citric acid decomposition pathway were inhibited,while the expressions of CitCSl and CitCS2 in citric acid synthesis pathway were up-regulated.